This disclosure relates to footwear in general and in particular to a cushioning device for footwear. In particular, it is concerned with such a device in the heel of footwear. Different devices are known to improve the comfort of footwear. Athletic footwear use different devices for improving the comfort during walking or running. This action usually starts with a heel strike followed with a rolling on to the midfoot and finally, the action of the forefoot. When the heel strikes, there can be forces involved on the ankle, knee and hip which flex to cushion and absorb the shock of the impact. The foot then rolls and turns inwardly in a process called pronation or outwardly in a process called supination. In other terms, the process of pronation or supination is the flattening out of the arch when the foot strikes the ground. Normally, the foot pronates or supinates to absorb shock when the heel hits the ground, and to assist in balance during mid-stance. The ankle tips or tilts towards the inside or outside of the foot.
Excessive pronation can be problematic because the shifting causes increased stress on the inside/medial aspect of the foot. It pulls on the stabilizing muscles in the lower leg (posterior tibialis) and often causes the knee to shift to the inside. The excessive stress on the body can overcompensate for this pronation and shift the ankle towards the outside causing the ankle to roll over.
Supination is the opposite motion of pronation. This occurs when the ankle tips or tilts outwards. This can cause difficulty in running and walking. A foot is in supination when the ankle is tipped to the outside.
Excessive supination predisposes the ankle to injury because the stabilizing muscles on the outside of the lower leg (peroneals) are in a stretched position. It does not take much force to cause the ankle to roll over, potentially causing ligament damage. Every person pronates and supinates. It is the body's way to absorb shock and allow the foot to work as a lever. Excessive motion in either direction can be problematic if not controlled.
In other situations, a foot may be prone to super-pronation. This is when a foot is not flat, but tilts slightly inwards or outwards. This can cause difficulty in running and walking.
It is desirable to absorb as much foot strike shock energy as possible consistent with stability and avoiding injury to the foot. It is also desirable to store shock energy and return it to the foot to facilitate energy transfer when the foot leaves the ground. It is also desirable to limit the tendency of the foot to over-pronate or over-supinate during the contact of the foot with the ground.
It is known to include spring devices in the soles of shoes. Spring devices in the heels store shock energy imparted by the foot strike during running and return a portion of that to the wearer's foot during foot lift. It is also known to provide longitudinal stiffening elements within a shoe to overcome or minimize the effect of over-pronation or over-supination during running.
None of the known devices provides for a good balance, cushion and shock absorption for the foot in a manner that minimizes the disadvantages and accounts for over-pronation or over-supination tendencies by reducing their effect.
This disclosure relates to a cushioning device which reduces the disadvantages of known systems and aids in the prevention of over-pronation or over-supination effects.